A locking and unlocking arrangement for reciprocating piston type actuators is described in U.S. Pat. No. 3,208,357. However, in such device the pressure fluid employed in connection with the actuator is independent of and functions separately from the pressure fluid that actuates the locking means. Where the actuator is a device such as a blowout preventer employed in water covered areas, particularly in connection with oil and gas wells, such arrangement is somewhat complicated and may create problems.
The construction and operation of a blowout preventer in connection with the drilling and production of an oil and gas well is well understood by those skilled in the art. Where such devices are employed in offshore operations, or in other water covered areas, the location of the blowout preventer is remote relative to the controls and so far as know to applicant, all devices currently in use, and including that which is shown in U.S. Pat. No. 3,208,357 requires four separate fluid operating lines in connection with controlling the various positions of the components.
For example, one control line is employed to operate the blowout preventer rams to move them to closed position; a second pressure fluid line extends from the remote control position into the water covered area or other somewhat substantial inaccessible location of the blowout preventer to lock the rams in closed position about a drill pipe or other well bore tubular member; a third line is employed to supply fluid pressure to the blowout preventer to unlock the arrangement which locks the rams in closed position; and yet a fourth line is emloyed to actuate the blowout preventer rams and retract them from closed position back to open position after the lock arrangement has been actuated to unlock the rams to accommodate such retraction.
The use of four separate fluid pressure conduits complicates the operation and use of a blowout preventer ram, or other similar piston type fluid actuator which is located in a remote location. Such lines may become fouled, damaged or other conditions may interfere with their satisfactory use. Some preventer constructions may severly restrict the practical use of lock arrangements presently used.